The regulation of grid frequency is a typical aspect about the management of interconnected grids. Production plans are daily prepared in order to have a load reserve available in case of an increase of load demand or to contrast sudden faults on the grid. In normal conditions specific production units are able to regulate the frequency by varying their load output, therefore grid frequency fluctuations are limited. In other cases the deviation of grid frequency from its nominal value may reach higher values, then all the connected generators are required to increase or decrease their load as function of the deviation from nominal speed and proportionally to their nominal load. It is to be noted that recently the typology of the power plants is rapidly changing; in fact it is getting more and more frequent the conversion of traditional plants into combined cycle power plants based on gas turbines, whose exhaust gases are recovered inside the boiler and used to generate the steam for the turbines; this allows the reaching of high specific power and efficiency. Due to the typical process of the steam generation inside the boiler, if the power plant is required to supply a rapid power change, it is to be considered that all the power will be supplied by the gas turbine during transient and only after a certain delay the steam turbine will have available the steam to increase its power output, for this to respect requirements about the frequency supports these plants must be operated at a lower load then the nominal, this implies a reduction in efficiency of all the cycle and a lower productivity. Since the participation in support of grid frequency is obligatory the capability of gas turbines in support rapid load variations is getting more important.
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